A conventionally-and frequently-employed column packing material has a chemical modification group 116 introduced into a silanol group 114 (Si—OH) group on the surface of a silica gel 112 by means of silylation of the silica gel using a silane compound having various chemical modification groups (FIG. 8[1]). A representative silane compound may for example be an octadecylchlorosilane compound, octylchlorosilane compound, butylchlorosilane compound, cyanopropylchlorosilane compound, phenylchlorosilane compound and the like, among which an octadecylchlorosilane compound is employed to introduce an octadecyl group to form a most frequently employed octadecyl silica gel packing material (ODS).
Any of these packing materials has substantial analytical advantages, but the effect of the silanol group 114 remaining on the surface of the substrate silica gel 112 is problematic. Thus, the residual silanol group 114 exhibits a strong interaction with a polar solute, especially with a basic solute, to adsorb the basic solute, resulting in a peak tailing which leads to a difficulty in obtaining a reliable reproducibility of the chromatogram.
On the other hand, the effect of the residual silanol group 114 was attempted to be reduced by an end-capping method in which a chemical modification group 116-carrying silica gel 112 is re-silylated by an end-capping agent such as trimethyl chlorosilane in a solvent such as toluene and then the residual silanol group 114 is bound chemically to a short alkyl group 122, but this end-capping allowed a substantial amount of the silanol group 114 to be still remaining (FIG. 8[2]).
Accordingly, it was proposed that the reaction between the silica gel and the end-capping agent is conducted in a gas phase instead of a solvent employed conventionally whereby obtaining a column packing material enabling an extremely low effect of the silanol group 114 on the surface of the silica gel 112 (JP-2611545).
Nevertheless, such a packing material involves a poor adhesion of the chemical modification group 116 and the short alkyl group 122 since these groups are bound individually to the silica gel surface although it is improved substantially with respect to the reduction in the residual silanol group 114, and, it is problematic also in terms of the durability because of the entirely exposed hydrophilic moiety of the silica gel 112.
An objective of the invention is to provide a column packing material having an excellent durability and exhibiting an extremely reduced effect of the residual silanol group, and a method for producing the same.